Cathode-ray tube commutator system



W. D. HOUGHTON CATHODE RAY TUBE COMMUTATOR SYSTEM Sent. 18. 1951 3Sheets-Sheet 5 Filed April 9, 1947 TIME - 5mm I wax 010mm FIRSTREVOLUT/Op TIME- INVENTOR. WILLIAM D. HOUGHTON ATTORNEY Patented Sept.18, 1951 asses CATHODE-RAY TUBE COMMUTATOR SYSTEM William D. Houghton,Port Jefferson, N. Y., assignor to Radio Corporation of America, a.corporation of Delaware Application April 9, 1947, Serial No. 740,375

14 Claims. 1

This invention relates to a multi-channel si nalling system, and moreparticularly to a multichannel printer telegraph system employing atelegraph code of the multi-unit type in which the units in each letteror symbol of the code are of equal length. Examples of such telegraphprinter codes are the conventional 5-unit and 'l-unit codes.

The invention is particularly applicable to a system employing pulseswhich are short compared to the time intervals between pulses. In such asystem, there is transmitted for each frame or cycle of operations atrain of pulses preceded or followed by a synchronizing pulse. Thepulses in each train are assigned to different channels. The intervalbetween two consecutive synchronizing pulses is divided into equal timeperiods, and the different time periods are respectively assigned todifferent channels.

A better understanding of the broad general principles of transmissionof the multi-channel system of the invention may be had b referring toFig. 1 which shows a train of short pulses transmitted for each frame orcycle of operations, as measured from the start or beginning of onesynchronizing pulse to the start or beginning of the succeedingsynchronizing pulse. The synchronizing period or time interval for eachcycle of operations includes a synchronizing pulse P and a series ofsequentially appearing channel pulses l to '7 inclusive, assuming thecase of only seven channels. The different pulses l to '7 representtransmission from different channels. Each channel has assigned to it atime interval which occurs at a difierent time from those assigned tothe other channels but the different time intervals assigned to thedifferent channels are equal. The solid line pulses indicate theposition within the assigned channel intervals that the channel pulseswould take when sending a mark signal, and the dotted line pulsesindicate their respective positions within these same assigned channelintervals when sending a space signal. It will thus be seen that thechannel pulse (which can be called the intelligence carrying pulse) mayoccupy one of two positions within the assigned channel interval,depending upon whether the pulse is to represent a mark or space signal.Preceding and succeeding frames or cycles of operation will includesimilar trains of pulses, each train including a synchronizing pulsefollowed by the seven channel pulses, in the assumption that sevenchannels are employed. The synchronizing period is identical for alltrains of pulses.

In the printer multi-channel system of the invention, the speed ofoperation of all pick-ups or auto heads are synchronized, as will appearin more detail hereinafter, and the repetition rate for the channelpulses is determined by the main sweep frequency which also controls thespeed of the tape in the printer pick-ups or auto heads.

Briefly stated, the present invention involves a novel type of cathoderay tube which electronically scans a plurality of sets or pairs oftargets for producing the channel pulses. The pairs of targets arespaced apart and arranged in a circle at a location corresponding tothat of the fluorescent screen in the conventional cathode ray tube. Theelectron beam is caused to traverse a circular path and to sequentiallypass over the different sets or pairs of targets. The different pairs oftargets are allotted to different channels. Each time the electron beammoves across a set or pair of targets, there is generated a pulse. Thepulse may occupy one of two positions and is generated when the electronbeam leaves one of the targets of a pair, but the position of theassociated pick-up relay for that particular channel determines whetherthe pulse is generated when the electron beam leaves the first or thesecond target of that pair. The targets of each set or pair are soarranged that the beam crosses first one target and then the other. Theposition of the pick-up relay is a function of whether the pick-up isscanning a mark or space signal element. The auto heads or pick-ups forthe different channels are driven by their respective motors at a speedwhich is synchronized with the repetition rate of the scanning sweep ofthe tube. Stated in other words, the driving voltage for the pick-ups orauto head motors is made synchronous with the main sweep or scanningfrequency, and each pick-up or auto head is retarded in phase slightly,by electrical or mechanical means well known in the art, so that at thetime of scanning the pick-up or auto head will be in the middle of itsmark or space signal element.

A more detailed description of the invention follows, in conjunctionwith a drawing, wherein:

Fig. 1 illustrates a series of pulses representative of the train ofpulses occurring for the output of the transmitter of the invention, foreach frame or cycle of operations;

Fig. 2 is a diagrammatic view, partly in section, of a cathode ray tubeand circuit therefor in accordance with one form of the invention;

Fig. 3 is a view of the target end of the beam tube of the invention asseen from the cathode or gun end;

Fig. 4 is a diagrammatic view, partly in section,

focussing anode.

3 of the target end of the beam tube and the circuit for producingpulses;

Fig. a is a detailed view showing a single pair or set of targets inrelation to the path of travel of the electron beam and to the electroncollector electrode;

Fig. 5b graphically illustrates the voltage wave form developed acrossthe load resistor I3 of Fig. 4;

Fig. 5c graphically ilustrates the pulses produced by differentiation ofthe waveform of Fig. 5b;

Fig. 6 graphically illustrates a modified voltage waveform which may beapplied to the deflection plates of the cathode ray tube of theinvention;

Fig. 7 illustrates the sweep circuit which may be used to apply thewaveform of Fig. 6 to the deflection plates of the beam tube, and

Fig. 8 illustrates a modified form of target construction for the beamtube when using the defleeting voltage of Fig. 6.

Fig. 2 shows a cross section of the cathode ray tube of the invention inassociation with part of the circuit employed 'in the transmitterarrangement. This cathode ray tube comprises a glass envelope I whichencloses an electron gun I shown within the dashed line box. This gun Iis well known in the art and comprises the usual cathode, a multiplicityof grids and an electron Two pairs of deflecting plates 28 and 28' areused to cause the electron beam to traverse a circular path over a groupof spaced sets or pairs of targets 9, '9. One pair of deflecting plates28 is fed by a sine wave oscillator 2 through leads 4 and 5, while theother pair of deflecting plates 28' are fed from the sameoscillator 2 ata 90 degree phase relation through a phase shifter 3 over leads 4 and B.The targets 9 and 9' of each channel are arranged as shown in moredetail in Figs. 3, 4 and 5a. The target 9 of each pair or set is locatedbetween the target 9 of the same set and the electron gun I and slightlyoverlaps the target 9', as shown. One set of targets 9 and 9' isallotted to each telegraph channel in the system. A common electroncollector disk I9 is placed in back of all of the targets 9 and 9' tocollect those electrons which do not strike the channel targets.

A frequency divider II is connected between the sine wave oscillator 2and the lead I22 eX- tending to the pick-up motors of the system of Fig.4. Such an arrangement enables the pickup motors to be synchronized withrespect to the scanning sweep frequency of the electron beam.

Fig. 4 shows the method of connecting the channel targets in a systememploying N number of channels.

The transmitter arrangement of Fig. 4 shows a plurality of sets or pairsof targets 9, 9, and associated with each channel a pick-up relay I2, anauto head or pick-up 40 for controlling the operation of the relay I2,and a motor I 2| for driving the pick-up or auto head 49. The variousmotors I2I for the different channels are connected through individualphase shifters 22 to the lead I22 which extends to the frequencyconverter II of Fig. 2. By suitable adjustment of the phase shifter 22associated with each channel, the pick-up for that channel will be inthe middle of its mark or'signal element at the time the beam ofelectrons strikes or scans the set of targets for that particularchannel.

All targets 9 of the difierent channels-are connected in parallel tolead I6 by means of connection 30. The other targets 9 of the diiferentchannels are connected to the armatures I9 of their respective pick-uprelays I2. A common load resistor I3 is connected between the lead I6and ground, and in circuit with this load resistor is a differentiatorcircuit comprising a resistor I5 and a condenser I4. The output from thesystem is taken off from lead M which may extend to a suitableamplifier, in turn, connected to a suitable radio frequency oscillator,not shown. The output from lead M is in the form of D. C. pulses whichmay be used to modulate a radio frequency transmitter, such as amagnetron. This 100% modulation may be amplitude, frequency or phasemodulation.

In explaining the operation of the system of Fig. 4, let it be assumedthat the electron beam is striking channel target 9 at point X (noteFigs. 3 and 5a), and the beam is being rotated in a clockwise directionalong path A. Electrons will then flow to target 9 and. through resistorI3 (Fig. 4) via lead I6. This will cause a negative voltage to bedeveloped across resistor I3 with respect to ground, assuming thatnegative potential is applied to the electron gun I in a manner employedin many conventional cathode ray circuits.

The negative voltage developed across resistor I3 will remain until theelectron beam crosses point Y in Figs. 3 and 5a. That is, the beamleaves target 9 at point Y and electrons flow to target 9. If thepick-up relay I2 is actuated at this time, this armature I9 will engagemakecontact I8, and the electrons which strike target 9 will flow toground through contacts I8 and I9, and the voltage developed acrossresistor I3 will cease. However, if printer relay I2 is not actuated,this armature I9 will engage contact 20, and electrons which striketarget 9' will flow via lead I! and through closed contacts I9 and 20 toresistor I3 via lead I 6. This will cause the negative voltage which wasdeveloped across resistor I3 when the electron beam struck target 9 toremain negative when the electron beam crosses point Y. The negativevoltage in this case will remain until the electron beam crosses point Z(note Figs. 3 and 5a) at which time the beam leaves target 9 and theelectrons flow to collector plate I9 and to ground. When the electronbeam leaves target 9', the negative voltage developed across resistor I3 will cease.

Fig. 5a shows a detail front view of one set or pair of channel targets9, 9' and the electron collector plate I0 as viewed from the electrongun. The electron beam is indicated by the circle at X and the path ofthe beam is indicated by the dashed line A. The arrow shows thedirection of travel or sweep of the electron beam.

Fig. 5b represents the voltage developed across resistor I3 as theelectron beam follows path A. The dashed line curve in Fig. 5brepresents the voltage wave which will result when relay I2 isunactuated and contacts I9 and 2!) closed While the electron beam istraversing target 9'. As Will be seen from Fig, 5b, when the electronbeam crosses point X at time R, a negative voltage is developed acrossresistor I3. This negative voltage continues until the beam reachespoint Y at time S, assuming that relay I2 (Fig. 4) is energized andoperated, in which case contacts I 8 and I9 will be closed. If pick-uprelay i2 is unactuated, contacts I9 and 20 will be closed and thenegative voltage will remain until the electron beam reaches point Z attime T, at which time the voltage developed across resistor I3 decreasesto zero. The duration of the negative pulse across resistor I3 will beequal to the time required for the electron beam to travel from point Xto point Y, or from point X to point Z depending upon the condition ofrelay l2.

The negative voltage developed across resistor I3 is differentiated bycondenser l4 and resistor 15 as a result of which sharply peaked voltageimpulses occur as shown in the curve of Fig. 50. When relay [2 isactuated, a pulse will appear in the mark position at time S, shown bythe solid line curve Fig. 50. When relay [2 is unactuated, the pulseshown in Fig. 5c in the mark position at time S will not appear but apulse will appear in the space position at time T, shown by the dashedline curve of Fig. 5c. The solid line negative pulse at time R in Fig.50 appears in the same position regardless of the condition of relay I2,but this pulse is not used in the utilization circuits connected to leadM in Fig. 4.

It will thus be seen that a pulse is formed each time the electron beamsweeps across a pair or set of targets 9 and 9, and the position of thepulse will depend upon the condition of the relay I2 associated withthat particular set 01' pair of targets.

The synchronizing pulse may be generated in numerous ways. As anexample, it may be generated in circuits external of the cathode raytube and combined with the channel pulses in the amplifier portion ofthe system. I prefer to use two closely spaced pulses forsynchroniaztion rather than a single pulse which is wider than thechannel pulses as shown in Fig. 1, although either kind ofsynchronization pulses may be used in the transmission system. If twosynchronizing pulses are used for each frame or cycle of operations,these should be more closely spaced than the channel pulses. One way ofproducing these two is to provide two closely spaced targets 8, 8 in themanner shown in Figs. 3 and 4. The spacing between targets 8, 8 iscloser than the spacing between any point Z on one set of channeltargets and the point Y on a following set of channel targets.

A modification of the invention is shown in Figs. 7 and 8 in which thecircular path of the electron beam on path A is made to jump to aninside ring and follow path B. (Note Fig. 8.) This is done by suddenlyreducing the amplitude of the sine wave voltage applied to thedeflecting plates of the cathode ray tube in such manner that thevoltage wave applied to the deflecting plates follows the curve shown inFig. 6. One way of doing this is shown in Fig.7.

Referring to Fig. 7, the output of the sine wave oscillator 2 is appliedto an amplifier 6 and also to a flip-flop gate generator 4. This gategenerator produces in lead 5 a square wave voltage of 50% mark and 50%space as shown by waveform 58. The gate 4 may be a self-restoringtrigger circuit. The mark time of the square wave 5!! is made equal tothe time of one complete cycle of oscillator 2, and the space time ofthe square wave 50 is also made to be equal to one complete cycle of theoscillator 2. This square wave 5 is applied to lead 5 in order to changethe gain of the amplifier B which is located between the oscillator 2and the phase shifter 3. Thus, for one complete cycle of oscillator 2,the circular beam trace will have one diameter while for the succeedingand preceding complete cycles the circular beam trace will have anotherdiameter.

Obviously, other types of sweep arrangements could be used with thesystem of the invention to obtain various types of combinations ofoutput pulses.

In using a sweep arrangement as shown in Fig. '7, in which the form ofthe sweep voltage wave applied to the deflecting plates is like thatshown in Fig. 6, the sets of targets for the different channels may havean arrangement like that shown in Fig. 8. The arrangement of Fig. 8enables the use of more sets of targets than can be provided on a.single diameter path of travel of the electron beam.

Although relatively few channels have been shown in the drawings, itshould be understood that as many channels may be used as desired. As anexample, it is possible in a large cathode ray tube to provide a hundredor more sets or pairs of targets 9 and 9 within a single envelope andthus connect the targets of a number of such cathode ray tubes inparallel using interlaced sweeping arrangements, as a result of whichthere may be employed many hundreds and perhaps thousands of channels.In the systems which use the invention, the motor drive for the pick-upor auto heads must be controlled with the sweep frequency so that eachprinter is in the middle of a baud when scanned by the tube of thisinvention.

An advantage of the system of the invention lies in the fact that theconstruction requires relatively few mechanical parts and provides asimple method of multiplexing a large number of telegraph channels.

If desired, more than two concentric rings of target plates could beused in practicing the invention, in which case the gain of amplifier 6,Fig. '7, would be changed to various levels sequentially in order tomake the beams scan past one ring and then the other. The number ofchanges in gain of amplifier 6 would be equal to the number ofconcentric rings of target plates.

The changes in gain of amplifier 5 could be accomplished by makingapparatus 4 of Fig. 7 produce a step wave output voltage. The length ofeach step would be made equal to the period of time required to scaneach ring or in other words equal to the period of 2.

What is claimed is:

1. A commutator cathode ray tube for use in a multiplex systemcomprising an electron gun, a plurality of physically spaced sets oftargets arranged in a circle, each set of targets comprising a pair ofplates spaced one behind the other and whose adjacent ends overlap,whereby first one target and then the other target of each set isadapted to be bombarded by the electron beam emanating from said gun assaid beam traverses a circular path, and means for causing the electronbeam to traverse a circular path whose diameter is the diameter of thecircle on which lie said sets of targets, whereby the sets of targetsare sequentially bombarded by the electron beam.

2. A cathode ray tube comprising a cathode for producing a stream ofelectrons, means focussing said stream into a beam, electron deflectingelements, a plurality of physically spaced sets of targets arranged in acircle, each set of targets comprising a pair of overlapping platesspaced one behind the other, and means coupled to said deflectingelements for causing said beam to traverse a circular path whosediameter is the diameter of the circle on which lie said sets oftargets.

3. A cathode ray tube comprising a cathode for producing a stream ofelectrons, means focussing said stream into a beam, electron deflectingelements, a plurality of, physically spaced sets of targets arranged ontwo concentric circles at one end of said tube, each set of targetscomprising a pair of overlapping plates spaced one behind the other, andmeans coupled to said deflecting elements for causing said beam toalternately traverse circular paths of difierent diameters correspondingto the diameters of said two concentric circles.

'4. A cathode ray tube comprising a cathode for producing a stream ofelectrons, means for focussing said stream into a beam, a plurality ofphysicall spaced sets of targets arranged end to end, each set oftargets comprising a pair of overlapping plates spaced one behind theother, and means coupled to said deflecting elements for causing saidbeam to bombard said sets of targets sequentially, whereby first onetarget and then the other target of each set is bombarded by the beam.

5. In a signalling system, a cathode ray tube having a cathode forproducing a stream of electrons, a pair of overlapping targets spacedfrom and positioned one behind the other, deflecting elements forcausing said stream of electrons to impinge on said targets insuccession, a relay under control of the intelligence to be sent outover said system, said relay having an armature, a break contact and amake contact in association with said armature, a connection from onetarget of said tube to said break contact, a connection from the othertarget of said tube to said armature, a load connected to one of saidlast connections, and a connection from said make contact to ground.

6. In a signalling system, a cathode ray tube having a cathode forproducing a stream of electrons, a pair of overlapping targets,deflecting elements for causing said stream of electrons to impinge onsaid targets in succession, a relay under control of the intelligence tobe sent out over said system, said relay having an armature, a breakcontact and a make contact in association with said armature, aconnection from one target of said tube to said break contact, aconnection from the other target of said tube to said armature, aresistor connected to said first connection, a differentiator circuitconnected to said resistor for difierentiating the voltage wavedeveloped across said resistor, a connection from said make contact toground, and means coupled to said diilerentiator circuit for utilizingthe output from said system.

7. In a signalling system, a cathode ra tube having a cathode forproducing a stream of eletrons, a pair of overlapping targets,deflecting elements for causing said stream of electrons to impinge onsaid targets in succession, a relay under control of a telegraphcircuit, said relay having an armature, a break contact and. a makecontact in association with said armature, a connection from said breakcontact to that target which is first impinged upon by said stream ofelectrons, means coupled to said connection for utilizing the outputfrom said system, a connection from said armature to said other target,and a connection from said make contact to ground.

8. In a signalling system, a cathode ray tube having a cathode forproducing a stream of electrons, a pair of overlapping targets,deflecting elements for causing said stream of electrons to impinge onsaid targets in succession, a relay under control'of a telegraphcircuit, said relay having an armature, a break contact, and a makecontact in association with said armature, a connection from said breakcontact to that target which is first impinged upon by said stream ofelectrons, a resistor coupled between said connection and ground, aconnection from said armature to said other target, a connection fromsaid make contact to ground, a differentiator circuit coupled to saidresistor for producing short pulses from the voltage wave developedacross said resistor, and means coupled to said differentiator circuitfor utilizing the output from said system.

9. In a multi-channel signalling system, a commutator cathode ray tubefor use in a multiplex system comprising an electron gun, a plurality ofphysically spaced sets of targets, one set for each channel, arranged ina circle, each set of targets comprising a pair of spaced plates whoseadjacent ends overlap, whereby first one target and then the othertarget of each set is adapted to be bombarded by the electron beamemanating from said gun, and means for causing the electron beam totraverse a circular path whose diameter is the diameter of the circle onwhich lie said sets of targets, whereby the sets of targets aresequentially bombarded by the electron beam, a relay in each channelunder control of keying mechanism for that channel, said relay having anarmature, a break contact and a make contact, means for connectingtogether all of the break contacts of all said relays and only thosetargets of said sets which are first bombarded by said beam, aconnection between the other target of each of said sets and thearmature of the particular relay for that channel, a connection from themake contact of each relay to ground, and a common load impedanceconnected to said break contacts.

10. In a multi-channel signalling system, a commutator cathode ray tubefor use in a multiplex system comprising an electron gun, a plurality ofphysically spaced sets of targets arranged end to end, each set oftargets comprising a pair of spaced plates whose adjacent ends overlap,whereby first one target and then the other target of each set isadapted to be bombarded by the electron beam emanating from said gun,and means for causing the electron beam to bombard said targetssequentially, said sets of targets being assigned to diiTerent channelsof said system, a relay in each channel under control of keyingmechanism for that channel, said relay having an armature, a breakcontact and a make contact, means for connecting together all of thebreak contacts of all said relays and only those targets of said setswhich are first bombarded by said beam, a connection between the othertarget of each of said sets and the armature of the particular relay forthat channel, a connection from the make contact of each relay toground, and a common load impedance connected to said break contacts.

11. In a multi-channel signalling system, a commutator cathode ray tubefor use in a multiplex system comprising an electron gun, a plurality ofphysically spaced sets of targets arranged in a circle, each set oftargets comprising a pair of spaced plates whose adjacent ends overlap,whereby first one target and then the other target of each set isadapted to be bombarded by the electron beam emanating from said gun,and means for causing the electron beam to traverse a circular pathwhose diameter is the diameter of the circle on which lie said sets oftargets, whereby the sets of targets are sequentially bombarded by theelectron beam, said sets of targets being assigned to different channelsof said system, a relay in each channel under control of keyingmechanism for that channel, said relay having an armature, a breakcontact and a make contact, means for connecting together all of thebreak contacts of all said relays and only those targets of said setswhich are first bombarded by said beam, a connection between the othertarget of each of said sets and the armature of the particular rela forthat channel, a connection from the make contact of each relay toground, circuits for synchronizing the operation of the keyingmechanisms in the different channels with the sweep of the electron gunin said cathode ray tube, and a common load impedance connected to saidfirst bombarded targets of said sets.

12. In a multi-channel signalling system, a commutator cathode ray tubefor use in a multiplex system comprising an electron gun, a plurality ofphysically spaced sets of targets arranged in a circle, each set oftargets comprising a pair of spaced plates whose adjacent ends overlap,whereby first one target and then the other target of each set isadapted to be bombarded by the electron beam emanatin from said gun, andmeans for causing the electron beam to traverse a circular path whosediameter is the diameter of the circle on which lie said sets oftargets, whereby the sets of targets are sequentially bombarded by theelectron beam, said sets of targets being assigned to different channelsof said system, a relay in each channel under control of keyingmechanism for that channel, said relay having an armature, a breakcontact and a make contact, means for connecting together all of thebreak contacts of all said relays and only those targets of said setswhich are first bombarded by said beam, a connection between the othertarget of each of said sets and the armature of the particular relay forthat channel, a connection from the make contact of each relay toground, circuits for synchronizing the operation of the keyingmechanisms in the 10 different channels with the sweep of the electrongun in said cathode ray tube, a common resistor connected to said firstbombarded targets of said sets, a difierentiator circuit connectedacross said resistor, and means coupled to said difierentiator circuitfor utilizing the output from said system.

13. A cathode ray tube comprising a cathode for producing a stream ofelectrons, means f0- cussing said stream into a beam, electrondeflecting elements, a plurality of physically spaced sets of targetsarranged on a plurality of concentric circles near one end of the tube,each set of targets comprising a pair of overlapping plates spaced onebehind the other, and means coupled to said deflecting elements forcausing said beam to sequentially traverse circular paths of differentdiameters corresponding to the diameters of said concentric circles.

14. A cathode ray tube comprising a cathode for producing a stream ofelectrons, means focussing said stream into a beam, electron deflectin;elements, a plurality of pairs of physically spaced targets arranged ontwo concentric circles, the targets of each pair being positioned behindone another and overlapping in their lengths. and means coupled to saiddeflecting elements for causing said beam to alternately traversecircular paths of difierent diameters corresponding to the diameters ofsaid two concentric circles.

WILLIAM D. I-IOUGH'ION.

REFERENCES CITED The following references are of record in the file ofthis patent:

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